Damper control apparatus

ABSTRACT

A damper control apparatus damps vibration of an unsprung member by controlling a damping force of a damper in a vehicle, the damper being interposed between a sprung member and the unsprung member. The damper control apparatus includes a vibration level detecting unit that detects a vibration level serving as a magnitude of the vibration of the unsprung member, and a stroke speed detecting unit that detects a stroke speed of the damper. The damper control apparatus further includes a command value calculating unit that determines a control command value, the control command value is a command value for controlling the damping force of the damper on the basis of the vibration level of the unsprung member and the stroke speed of the damper.

TECHNICAL FIELD

The present invention relates to a damper control apparatus.

BACKGROUND ART

A conventional damper control apparatus controls a damping force of adamper interposed between a sprung member and an unsprung member of avehicle. The damper control apparatus controls the damping force of thedamper by focusing on an expansion/contraction displacement and anexpansion/contraction speed of the damper, for example. This type ofdamper control apparatus suppresses rattling of the unsprung member bydetermining whether the damper is decelerating or accelerating, andincreasing a control gain so that the damper generates a large dampingforce when the damper is decelerating. When the damper is accelerating,on the other hand, the damper control apparatus improves a road surfacefollowing performance of the unsprung member by reducing the controlgain so that the damper generates a small damping force. As a result,passenger comfort in the vehicle is improved (see JP2007-210590A).

A different type of damper control apparatus controls the damping forceof the damper by focusing on a frequency and an amplitude of anexpansion/contraction acceleration of the damper, for example. This typeof damper control apparatus improves the passenger comfort of thevehicle by determining a road surface condition, selecting anappropriate damping force map for the road surface condition, andcontrolling the damping force of the damper in accordance with theselected damping force map (see JP2002-144837A).

SUMMARY OF INVENTION

Although the damper control apparatuses described above use differentcontrol methods, both improve the passenger comfort of the vehicle byperforming control that is appropriate for a vibration condition of theunsprung member.

With the technique disclosed in JP2007-210590A, however, a damping forcetarget value is simply determined by multiplying theexpansion/contraction speed by the expansion/contraction displacementand then multiplying a resulting value by a control gain that iscommensurate with the value, without taking the magnitude of thevibration into account. Likewise with the technique disclosed inJP2002-144837A, the damping force is simply increased by increasing acurrent command steadily as the road surface deteriorates. With thedamper control apparatuses described above, therefore, controlcorresponding to the magnitude of the vibration of the unsprung memberis not performed, leaving room for improvement in the passenger comfortof the vehicle.

It is therefore an object of the present invention to provide a dampercontrol apparatus that improves passenger comfort in a vehicle.

A damper control apparatus according to an embodiment of the presentinvention is configured to damp vibration of an unsprung member bycontrolling a damping force of a damper in a vehicle, the damper beinginterposed between a sprung member and the unsprung member. The dampercontrol apparatus includes a vibration level detecting unit configuredto detect a vibration level, the vibration level serving as a magnitudeof vibration of the unsprung member, and a stroke speed detecting unitconfigured to detect a stroke speed of the damper. The damper controlapparatus also includes a command value calculating unit configured todetermine a control command value on the basis of the vibration level ofthe unsprung member and the stroke speed of the damper, the controlcommand value being a command value for controlling the damping force ofthe damper.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a view showing a configuration of a damper control apparatusaccording to an embodiment of the present invention.

FIG. 2 is a view illustrating a system of an object serving as adetection subject.

FIG. 3 is a view showing a configuration of a vibration level detectingunit.

FIG. 4 is a view illustrating a resultant vector of a first referencevalue and a second reference value.

FIG. 5 is a view illustrating a locus of the first reference value andthe second reference value and a locus of the first reference value anda third reference value.

FIG. 6 is a view showing example of maps set in a command valuecalculating unit.

FIG. 7 is a view showing damping characteristics of a damper atrespective vibration levels of the unsprung member.

FIG. 8 is a view showing a relationship between a current amount and adamping coefficient, which is stored in a damping force adjustment unit.

DESCRIPTION OF EMBODIMENTS

An embodiment of the present invention will be described below withreference to the attached figures.

In this embodiment, as shown in FIG. 1, a damper control apparatus Econtrols a damping force generated by a damper D provided in a vehicle.The damper D is interposed between a sprung member B and an unsprungmember W constituting the vehicle. The damper D includes a damping forceadjustment unit 4 that generates the damping force in response to anexpansion/contraction operation of the damper D.

The damper control apparatus E includes a vibration level detecting unit1 that detects a vibration level r indicating a magnitude of vibrationof the unsprung member W, and a stroke speed detecting unit 2 thatdetects a stroke speed Vd of the damper D. The damper control apparatusE also includes a command value calculating unit 3 that determines acontrol command value I on the basis of the vibration level r of theunsprung member W, the vibration level r being detected by the vibrationlevel detecting unit 2, the control command value I being a command linefor controlling the damping force of the damper D, and the stroke speedVd of the damper D, detected by the stroke speed detecting unit 2. Thedamper control apparatus E further includes a driving unit 5 thatsupplies a current to the damping force adjustment unit 4 in accordancewith the control command value I determined by the command valuecalculating unit 3.

In this example, the damper D is provided in the vehicle so as to beinterposed between the sprung member B and the unsprung member W anddisposed parallel to a suspension spring VS. The sprung member B iselastically supported by the suspension spring VS. The unsprung member Wincludes a vehicle wheel and a link, which are attached to the sprungmember B to be capable of swinging.

As shown in FIG. 2, the damper D is constituted by a fluid pressuredamper, for example.

In FIG. 2, the damper D includes a cylinder 12, a piston 13 insertedinto the cylinder 12 to be free to slide, and a piston rod 14 insertedinto the cylinder 12 to be free to move and coupled to the piston 13.The damper D further includes two pressure chambers 15 and 16 definedwithin the cylinder 12 by the piston 13, a passage 17 connecting therespective pressure chambers 15 and 16 to each other, and the dampingforce adjustment unit 4, which applies a resistance force to a flow offluid passing through the passage 17. With this configuration, thedamper D forms a fluid pressure damper.

When fluid charged into the pressure chambers 15 and passes through thepassage 17 in response to an expansion/contraction operation of thedamper D, resistance is applied to the fluid passing through the passage17 by the damping force adjustment unit 4. Accordingly, a damping forcefor suppressing the expansion/contraction operation of the damper D isgenerated, and as a result, relative movement between the sprung memberB and the unsprung member W can be suppressed.

In this example, a magnetorheological fluid is used as the fluid chargedinto the pressure chambers 15 and 16. The damping force adjustment unit4 is configured to be capable of applying a magnetic field to thepassage 17, and adjusts the magnitude of the magnetic field applied tothe passage 17 in accordance with a current amount supplied thereto fromthe driving unit 5 of the damper control apparatus E. Accordingly, theresistance force applied to the flow of magnetorheological fluid passingthrough the passage 17 varies, and as a result, the damping force of thedamper D can be varied.

Hence, the damper control apparatus E controls the damping force of thedamper D by increasing and reducing the current supplied to the dampingforce adjustment unit 4.

It should be noted that when an electrorheological fluid is used as thefluid, the damping force adjustment unit 4 may be configured to becapable of applying an electric field to the passage 17. For example,the damping force adjustment unit 4 varies the damping force generatedby the damper D by adjusting the magnitude of the electric field inaccordance with a voltage supplied thereto from the damper controlapparatus E so as to vary the resistance force applied to the fluidflowing through the passage 17.

Furthermore, working oil, water, an aqueous solution, a gas, and so onmay be used as the fluid instead of the magnetorheological fluid orelectrorheological fluid described above. In these cases, the dampingforce adjustment unit 4 is constituted, for example, by a damping valvethat varies a flow passage area of a passage (not shown) newly providedin the damper D, and an actuator having a high control response, such asa solenoid, that can adjust the flow passage area of the passage bydriving a valve body of the damping valve. The damper control apparatusE adjusts the flow passage area of the passage by increasing andreducing a current amount applied to the actuator, with the result thatthe resistance force applied to the fluid flowing through the passagevaries. In so doing, the damper control apparatus E can adjust thedamping force generated by the damper D.

Further, when the fluid is a liquid and the damper D is a single rodtype damper, a gas chamber, a reservoir, and so on are provided in thedamper D to compensate for a volume by which the piston rod 14 entersand exits the cylinder 12. When a gas is used as the fluid instead of aliquid, the gas chamber, reservoir, and so on need not be provided.

Alternatively, a uniflow type damper may be used as the damper D. Inthis case, a reservoir is provided in the damper D, and the damper D isconfigured such that the fluid is discharged from the interior of thecylinder 12 through a passage communicating with the reservoir duringboth expansion and contraction of the damper D. The damping forceadjustment unit 4 is provided midway in the passage extending from thecylinder 12 to the reservoir, and the damping force is generated byapplying resistance to the flow of the fluid.

Furthermore, an electromagnetic damper that generates the damping forcefor suppressing relative movement between the sprung member B and theunsprung member W using an electromagnetic force may be used as thedamper D instead of the configurations described above. For example, theelectromagnetic damper may be constituted by a motor and a motionconversion mechanism that converts a rotary motion of the motor into alinear motion, or by a linear motor. When the damper D is anelectromagnetic damper, the damping force adjustment unit 4 functions asa motor driving apparatus that adjusts a current flowing to the motor orthe linear motor.

The vibration level detecting unit 1, the command value calculating unit3, and the damping force adjustment unit 4 will now be described.

First, the vibration level detecting unit 1 will be described in detail.To simplify the description, a principle of a method used by thevibration level detecting unit 1 to detect the vibration level of theunsprung member W will be described.

First, a case in which the vibration level of an object M is detected bythe vibration level detecting unit 1 in a system shown in FIG. 3, inwhich the object M is supported by a spring S, will be considered. FIG.3 shows a spring mass system in which the object M is supportedelastically from below in the figure by the spring S, which is attachedvertically to a base T.

Here, a method of detecting an overall vibration level of the object Min an up-down direction of FIG. 3, or in other words an orthogonaldirection to a plane of the base T, will be described. To detect theup-down direction vibration level of the object M, it is necessary toobtain an up-down direction speed of the object M, set the obtainedvalue as a first reference value a, and obtain a second reference valueb corresponding to a differential value or an integral value of thefirst reference value a. The vibration level r of the unsprung member Wis then determined using the first reference value a and the secondreference value b.

In a case where the first reference value a is set as the up-downdirection speed of the object M, the up-down direction speed of theobject M may be obtained by, for example, attaching an accelerationsensor to the object M, detecting an up-down direction acceleration ofthe object M using the acceleration sensor, and integrating the detectedup-down direction acceleration.

When an up-down direction displacement of the object M corresponding tothe integral value of the first reference value a is set as the secondreference value b, the up-down direction displacement of the object Mmay be obtained by integrating the first reference value a, and theobtained displacement may be set as the second reference value b.

When a value corresponding to the differential value of the firstreference value a is set as the second reference value b, or in otherwords when the second reference value b is set to obtain the up-downdirection acceleration of the object M, the up-down directionacceleration may be obtained from the aforementioned accelerationsensor, and the obtained acceleration may be set as the second referencevalue b. Alternatively, the second reference value b may be obtained byproviding a differentiator and differentiating the first reference valuea.

Further, to enable detection of a vibration level of an arbitraryfrequency band, from among the vibration levels of the detection subjectobject M, a detection subject frequency component may be extracted fromthe first reference value a and the second reference value b.

More specifically, the detection subject frequency component of thefirst reference value a and the second reference value b can be obtainedby filtering the first reference value a and second reference value busing a band pass filter or the like. Basically, high-spectral-densityvibration of the object M can be extracted by employing a band passfilter that extracts an identical frequency to a natural frequency ofthe spring mass system constituted by the object M and the spring S.

A band pass filter is capable of extracting only vibration in a specificevaluation subject frequency band, and can therefore be used to removenoise and the like superimposed on the vibration of the object M.However, in a case where the object M vibrates in a single period, forexample, the band pass filter may be omitted.

Incidentally, vibration of the object M at an arbitrary frequency may beexpressed by a sine wave. An arbitrary frequency component of the firstreference value a, i.e. the speed of the object M, can also be expressedby a sine wave. For example, when an arbitrary frequency component ofthe first reference value a is expressed by sin ωt (where ω is anangular frequency and t is time), −(1/ω) cos ωt is obtained byintegrating sin ωt. Further, when an amplitude of the first referencevalue a is compared with an amplitude of a resulting integral value, theamplitude of the integral value is 1/ω times the first reference valuea.

Hence, when the second reference value b corresponds to the integralvalue of the first reference value a, respective amplitudes of the firstreference value a and the second reference value b can be adjusted(corrected) to equal values by multiplying the value corresponding tothe integral value of the first reference value a by ω using the angularfrequency ω that matches the frequency extracted by the filter.

Further, when the second reference value b corresponds to thedifferential value of the first reference value a, the respectiveamplitudes of the first reference value a and the second reference valueb can be adjusted (corrected) to equal values by multiplying the valuecorresponding to the differential value of the first reference value aby 1ω.

To determine the vibration level r, therefore, the angular frequency ωof the detection subject vibration is used to correct the respectiveamplitudes of the first reference value a and the second reference valueb to identical values. When the second reference value b corresponds tothe integral value of the first reference value a, the valuecorresponding to the integral value of the first reference value a ismultiplied by co, and when the second reference value b corresponds tothe differential value of the first reference value a, the valuecorresponding to the differential value of the first reference value ais multiplied by 1/ω.

Next, the first reference value a and second reference value b processedin the manner described above are plotted on orthogonal coordinates, asshown in FIG. 4, whereupon a length of a resultant vector U of the firstreference value a and second reference value b plotted on the orthogonalcoordinates is calculated and set as the vibration level r.

The length of the resultant vector U corresponds to a value of a squareroot of a sum of squares of the first reference value a and secondreference value b, and can be determined from (a²+b²)^(1/2).Alternatively, a root calculation may be omitted such that a value(a²+b²) of a sum of squares is determined as the length of the resultantvector U.

Hence, a value from which the length of the resultant vector U can beestimated, or in other words a value having a correlative relationshipwith the length of the resultant vector U, may be determined and used asthe vibration level r. In so doing, a root calculation having a highload can be avoided, and as a result, a calculation time can beshortened.

It should be noted that a value obtained by raising the length of theresultant vector U to the power of z (where z is an arbitrary value) anda value obtained by multiplying the length by an arbitrary coefficient,while not directly matching the length of the resultant vector U, arevalues from which the length of the resultant vector U can berecognized. Needless to mention, these values may also be used as thevibration level r. In other words, any value from which the length ofthe resultant vector U can be recognized may be used as the vibrationlevel r.

Here, when the object M is caused to vibrate by up-down movement of thebase T or by applying and removing displacement to and from the objectM, the spring S expands and contracts such that one energy conversionfrom an elastic energy of the spring S to a kinetic energy of the objectM and the other energy conversion from the kinetic energy of the objectM to the elastic energy of the spring S are performed alternately.Therefore, in the absence of outside disturbances, a speed of the objectM when the object M is maximally displaced from a neutral position is 0(zero), and when the object M is in the neutral position, the speed ofthe object M is at a maximum. It should be noted that the neutralposition is a position of the object M when elastically supported by thespring S in a static condition.

The respective amplitudes of the first reference value a and the secondreference value b are equalized by the correction procedure describedabove such that the first reference value a and the second referencevalue b deviate from each other by a phase difference of 90 degrees.Hence, when the vibration of the object M is not damped such that theobject M vibrates repeatedly in an identical manner, a locus formed bythe first reference value a and the second reference value b ideallydepicts a perfect circle, as shown in FIG. 4. The vibration level r canbe understood to be equal to a radius of this circle.

It should be noted that in actuality, it may be impossible to align therespective amplitudes with each other perfectly due to an extractionprecision of the filter, outside disturbances acting on the object M,and noise included in the first reference value a, second referencevalue b, and so on. However, the value of the vibration level r issubstantially equal to the radius of the aforementioned circle.

Hence, when the first reference value a representing the speed of theobject M is 0, an absolute value of the second reference value brepresenting the displacement of the object M takes a maximum value, andconversely, when the second reference value b is 0, an absolute value ofthe first reference value a takes a maximum value. Therefore, when thevibration condition of the object M does not vary, the vibration level rideally takes a fixed value.

In other words, the vibration level r is a value that serves as an indexexpressing the vibration amplitude of the object M, and thereforeexpresses the magnitude of the vibration.

As is evident from the procedures described above, when calculating thevibration level r, there is no need to determine a wave height bysampling one of the displacement, the speed, and the acceleration of theobject M within a single period, and only the displacement and speed ofthe object M need be obtained. Hence, the vibration level r can bedetermined in a timely fashion. In other words, by detecting thevibration level r in the manner described above, the magnitude of thevibration of the object M can be detected in a timely fashion and inreal time.

The vibration level r may also be determined by setting any relationship(combination) from among combinations of the speed and acceleration ofthe object M, the acceleration and an acceleration variation rate of theobject M, and the displacement of the object M and a value correspondingto an integral value of the displacement as the first reference value aand the second reference value b.

Likewise with these settings, the first reference value a and the secondreference value b deviate from each other by a phase difference of 90degrees, and therefore, by adjusting (correcting) the second referencevalue b using the angular frequency co of the detection subjectvibration, the locus obtained when the first reference value a and thesecond reference value b are plotted on orthogonal coordinates depicts acircle. The radius of the circle depicted on the orthogonal coordinatesis determined as the vibration level r, and the vibration level r servesas an index expressing the magnitude of the vibration.

In other words, by setting the first reference value a as any one of thedisplacement, the speed, and the acceleration in a direction matching adirection of the detection subject vibration of the object M, andsetting the second reference value b as a value corresponding to theintegral value or the differential value of the first reference value a,the vibration level r of the unsprung member W can be determined.

The first reference value a may be obtained by differentiating orintegrating a signal output from a sensor instead of being obtaineddirectly from the sensor.

The second reference value b may be obtained directly from a sensor. Forexample, instead of obtaining the second reference value b bydifferentiating or integrating the first reference value a in a casewhere a value corresponding to the differential value or a valuecorresponding to the integral value of the first reference value a isset as the second reference value b, a separate sensor may be providedsuch that the second reference value b is obtained directly from thesensor.

Further, a plurality of vibration levels may be calculated from acombination of different parameters, whereupon the final vibration levelr is determined.

For example, in a case where the value corresponding to the integralvalue of the first reference value a is set as the second referencevalue b, a value corresponding to the vibration level r may bedetermined in accordance with the procedures described above using thefirst reference value a and the second reference value b, and this valuemay be set as a first vibration level r1.

In addition, the value corresponding to the differential value of thefirst reference value a is set as a third reference value c, whereupon avalue corresponding to the vibration level r is determined in accordancewith the procedures described above using the first reference value aand the third reference value c rather than the first reference value aand the second reference value b, and this value is set as a secondvibration level r2.

An average value of the first vibration level r1 and the secondvibration level r2 is then calculated by adding together the firstvibration level r1 and the second vibration level r2 and dividing theresult by “2”, and the resulting average value may be set as thevibration level r.

In a case where the value corresponding to the differential value of thefirst reference value a is set as the second reference value b, thevalue corresponding to the integral value of the first reference value amay be set as the third reference value c.

The above example will now be described with reference to FIG. 5. Asshown in FIG. 5, orthogonal coordinates in which the first referencevalue a is plotted on the abscissa and the second reference value b andthird reference value c are plotted on the ordinate will be considered.A circle H having a maximum value of the first reference value a as aradius is indicated in FIG. 5 by a dotted line.

To determine a vibration level of a detection subject frequency bandfrom among the vibration levels of the object M, the first referencevalue a, second reference value b, and third reference value c arefiltered using a band pass filter, as described above.

In this case, when a deviation occurs between the frequency extracted bythe band pass filter and the vibration frequency of the object M suchthat the first vibration level r1 takes a value equal to or larger thanthe maximum value of the first reference value a, a locus J of the firstreference value a and the second reference value b forms an ellipse thatis larger than the circle H. The second vibration level r2, on the otherhand, takes a value equal to or smaller than the maximum value of thefirst reference value a, and therefore a locus K of the first referencevalue a and the third reference value c forms an ellipse that is smallerthan the circle H.

In other words, in a condition where the vibration frequency of theobject M and the detection subject vibration frequency do not match, adeviation occurs in the procedures described above between the angularfrequency co used during the correction and an actual angular frequencyω′.

Accordingly, a maximum value of the second reference value b followingadjustment of the second reference value b corresponding to the integralvalue of the first reference value a is ω/ω′ times the maximum value ofthe first reference value a, and a maximum value of the third referencevalue c corresponding to the differential value of the first referencevalue a following adjustment is ω′/ω times the maximum value of thefirst reference value a.

Hence, when the first vibration level r1 takes a larger value than thefirst reference value a, the second vibration level r2 takes acorrespondingly smaller value than the first reference value a, andtherefore, by averaging the first vibration level r1 and the secondvibration level r2 in order to determine the vibration level r,variation in the vibration level r can be absorbed. In other words, anerror in the vibration level r can be reduced.

The vibration level r can therefore be determined with stability evenwhen the vibration frequency of the object M and the detection subjectvibration frequency do not match, and as a result, a favorable detectionresult can be obtained in relation to the vibration level r.

Furthermore, when an undulation occurs in the vibration level r and itis known that noise of a frequency component twice as large as thevibration frequency of the object M is superimposed on the vibrationlevel r, the vibration level r may be filtered using a filter thatremoves the superimposed noise.

An example in which the vibration level r is determined by setting thevalue corresponding to the integral value of the first reference value aand the value corresponding to the differential value of the firstreference value as the second reference value b and the third referencevalue c, respectively, was described above, but the present invention isnot limited to this example.

For example, a vibration level r1 may be determined by setting thedisplacement of the object M as the first reference value a and settingthe speed of the object M as the second reference value b, whereupon aseparate, additional vibration level r2 is determined by setting theacceleration of the object M as the first reference value a and settingthe acceleration variation rate of the object M as the second referencevalue b.

An average value of the vibration level r1 obtained from therelationship between the displacement and the speed of the object M andthe vibration level r2 obtained from the relationship between theacceleration and the acceleration variation rate of the object M maythen be determined as the final vibration level r.

Hence, a plurality of combinations of two parameters used as the firstreference value and the second reference value may be set, and on thebasis of a plurality of vibration levels obtained from the respectiveparameters, a value such as an average value of the respective vibrationlevels, for example, may be obtained as the final vibration level r.

Next, an embodiment in which the vibration level detecting unit 1 isapplied to a vehicle to detect the vibration level r of the unsprungmember W provided in the vehicle will be described with reference toFIG. 1.

As shown in FIG. 1, the vibration level detecting unit 1 detects thevibration level r of the unsprung member W. The vibration leveldetecting unit 1 obtains the stroke speed Vd of the damper D, output bythe stroke speed detecting unit 2, as the first reference value.

The vibration level detecting unit 1 includes a second reference valueacquiring unit 21 that obtains the value corresponding to thedifferential value of the first reference value as the second referencevalue, and a third reference value acquiring unit 22 that obtains thevalue corresponding to the integral value of the first reference valueas the third reference value.

Further, the vibration level detecting unit 1 includes a filter 23 thatextracts a resonance frequency component of the unsprung member W fromthe first reference value, second reference value, and third referencevalue, and an adjustment unit 24 that adjusts the first reference value,second reference value, and third reference value relative to eachother. The vibration level detecting unit 1 also includes a vibrationlevel calculating unit 25 that determines the vibration level r of theunsprung member W.

It should be noted that since the first reference value is the strokespeed Vd of the damper D itself, obtained from the stroke speeddetecting unit 2, the stroke speed Vd output by the stroke speeddetecting unit 2 is input as is into the filter 23.

The stroke speed detecting unit 2 includes a stroke sensor 26 thatdetects a stroke displacement of the damper D, and a differentiator 27that calculates the stroke speed Vd of the damper D by differentiatingthe stroke displacement of the damper D, detected by the stroke sensor26.

The stroke speed detecting unit 2 sets the detected stroke speed Vd asthe first reference value, and outputs the first reference value to thevibration level detecting unit 1.

It should be noted that since, in this embodiment, the stroke speeddetecting unit 2 is provided in the damper control apparatus E and thestroke speed Vd detected by the stroke speed detecting unit 2 is used asthe first reference value, a first reference value acquiring unit forobtaining the first reference value is not provided in the vibrationlevel detecting unit 1. However, in a case where a sensor is attached tothe unsprung member W such that the up-down direction acceleration,speed, or displacement of the unsprung member W is detected directly andused as the first reference value, a first reference value acquiringunit for obtaining a detection signal output by the sensor as the firstreference value may be provided.

The second reference value acquiring unit 21 determines a damperacceleration αd, which is a stroke acceleration of the damper D, bydifferentiating the first reference value, i.e. the stroke speed Vd ofthe damper D, and sets the damper acceleration αd as the secondreference value. The second reference value acquiring unit 21 thenoutputs the second reference value to the filter 23.

The third reference value acquiring unit 22 determines a damperdisplacement Xd, which is the stroke displacement of the damper D, byintegrating the first reference value, i.e. the stroke speed Vd of thedamper D, and sets the damper displacement Xd as the third referencevalue. It should be noted that since the damper displacement Xd is alsodetected by the stroke sensor 26, the detected damper displacement Xdmay be used as is as the third reference value. The third referencevalue acquiring unit 22 outputs the third reference value to the filter23.

The filter 23 filters the stroke speed Vd of the damper D serving as thefirst reference value, the damper acceleration αd serving as the secondreference value, and the damper displacement Xd serving as the thirdreference value. In this embodiment, the filter 23 extracts only afrequency component in the resonance frequency band of the unsprungmember W from the stroke speed Vd, the damper acceleration αd, and thedamper displacement Xd of the damper D. As a result, valuescorresponding respectively to the stroke speed Vd, the damperacceleration αd, and the damper displacement Xd are obtained.

In a case where the first reference value is differentiated andintegrated in order to obtain the second reference value and the thirdreference value when determining the displacement, speed, andacceleration of the unsprung member W, filter processing may beperformed using the filter 23 on only the damper displacement Xd priorto acquisition of the first reference value.

In other words, filter processing may be performed directly on theoutput of the stroke sensor 26, or performed on the first referencevalue alone before obtaining the second reference value and the thirdreference value. The first reference value, second reference value, andthird reference value obtained in this manner are then adjusted in theadjustment unit 24 using the angular frequency co that matches theresonance frequency of the unsprung member W.

The vibration level calculating unit 25 calculates the first vibrationlevel r1 from the first reference value and the second reference value,calculates the second vibration level r2 from the first reference valueand the third reference value, and determines an average value thereofas the vibration level r of the unsprung member W. The vibration level rof the unsprung member W may be determined from the first referencevalue and the second reference value without providing the thirdreference value acquiring unit 22, but by determining the vibrationlevel r using the third reference value acquiring unit 22, a morefavorable detection result is obtained in relation to the vibrationlevel r.

In this example, the command value calculating unit 3 adjusts a dampingcoefficient of the damper D in accordance with a current amount suppliedto the damping force adjustment unit 4. The command value calculatingunit 3 determines a current value I as the control command value to beapplied to the damping force adjustment unit 4 from the vibration levelr determined in the manner described above and the stroke speed Vddetected by the stroke speed detecting unit 2. The driving unit 5includes a PWM (Pulse Width Modulation) circuit or the like, forexample, and supplies a current amount corresponding to the currentvalue I determined by the command value calculating unit 3 to thedamping force adjustment unit 4.

More specifically, the command value calculating unit 3 holds aplurality of maps representing a relationship between the stroke speedVd and the current value I serving as variable parameters. As shown inFIG. 6, for example, maps M1 to M4 determined for respective vibrationlevels r of the unsprung member W are stored in the command valuecalculating unit 3.

The command value calculating unit 3 selects a map on the basis of thevibration level r calculated by the vibration level calculating unit 25,and performs a map calculation from the stroke speed Vd detected by thestroke speed detecting unit 2 while referring to the selected map. Inthe map calculation, the command value calculating unit 3 calculates thecurrent value I associated with the detected stroke speed Vd from theselected map, and outputs a control command to the driving unit 5 tocause the driving unit 5 to output a current corresponding to thecurrent value I to the damping force adjustment unit 4.

The plurality of maps held by the command value calculating unit 3 arebasically set such that as the vibration level r increases, an inclineof a characteristic between the control command value relating to thedamper D and the stroke speed Vd steadily increases.

More specifically, the vibration level r is classified as “high”,“medium”, “low”, and “0” according to the magnitude of the vibrationlevel r, and maps corresponding to the respective classifications areprepared.

For example, when the detected vibration level r is classified as“high”, the command value calculating unit 3 selects the map M1corresponding to the “high” classification from the group of maps M1 toM4 shown in FIG. 6, and determines the current value I serving as thecontrol command value from the stroke speed Vd using the selected mapM1.

Similarly, when the vibration level r is classified as “medium”, thecommand value calculating unit 3 selects the map M2 corresponding to the“medium” classification from the group of maps, and determines thecurrent value I from the stroke speed Vd using the selected map M2.

Further, when the vibration level r is classified as “low”, the commandvalue calculating unit 3 selects the map M3 corresponding to the “low”classification from the group of maps, and determines the current valueI from the stroke speed Vd using the selected map M3.

Furthermore, when the vibration level r is classified as “0”, thecommand value calculating unit 3 selects the map M4 corresponding to the“0” classification from the group of maps, and determines the currentvalue I from the stroke speed Vd using the selected map M4.

The classifications of the vibration level r may be set as desired. Forexample, the vibration level r may be set in the “0” classification whenthe value thereof is 0, in the “low” classification when the valuethereof is 0<r<0.3, in the “medium” classification when the valuethereof is 0.3≦r<0.6, and in the “high” classification when the valuethereof is 0.6≦r.

Alternatively, instead of classifying the vibration level r, maps fromwhich optimum current values I can be determined may be prepared inadvance respectively for cases in which the vibration level r is “0”,“0.1”, “0.3”, and “0.6”, for example.

For example, when the vibration level r is 0.4, the current value I maybe determined by performing a linear interpolation using two maps,namely the optimum map when the vibration level r is “0.3” and theoptimum map when the vibration level r is “0.6”. In other words, currentvalues I may be determined respectively from the maps for the 0.3vibration level and the 0.6 vibration level, and the current value I fora vibration level r of 0.4 may then be determined from these currentvalues I.

Further, on the maps M1, M2, M3, M4, a contraction side characteristicof the damper D, in which the stroke speed Vd takes a positive value,and an expansion side characteristic of the damper D, in which thestroke speed Vd takes a negative value, are asymmetrical.

Furthermore, in an expansion side range and a contraction side range ofthe maps M1, M2, M3, the incline of the map is set to increase steadilyas the vibration level r increases. Moreover, the current value I (avalue of an intercept on the characteristic lines of the maps M1, M2,M3) of the map in a case where the stroke speed Vd is 0 is set to becomesteadily larger as the vibration level r increases.

The maps M1, M2, M3, M4 may be set such that the contraction sidecharacteristic of the damper D, in which the stroke speed Vd takes apositive value, and the expansion side characteristic of the damper D,in which the stroke speed Vd takes a negative value, are symmetrical.The maps M1, M2, M3, M4 may be set optimally in accordance with thevehicle in which the damper control apparatus E is installed.

Further, the map M3 is used in a condition where the vibration level ris small such that the damper D vibrates slightly. On the map M3, thecurrent value I is set at a predetermined value larger than that of theother maps such as the map M2 so that when the stroke speed Vd is intransition in the vicinity of 0 (zero), the damper D is actively causedto generate a damping force. In so doing, throbbing vibration of theunsprung member W can be sufficiently suppressed. As a result, throbbingvibration is not transmitted to vehicle passengers.

The map M4 is selected when the vibration level r is 0. If the currentvalue I is set similarly to that of the map M3 when the vibration levelr is 0, the damping force generated when the stroke speed Vd of thedamper D is in the vicinity of 0 becomes too large, and as a result, ajiggling is transmitted to the vehicle passengers, leading to areduction in passenger comfort. The jiggling is constituted by smallup-down vibratory movements caused by overdamping in a frequency bandbetween sprung mass resonance and unsprung mass resonance.

To solve this problem, on the map M4, the current value I employed whenthe stroke speed Vd is in the vicinity of 0 is set at a predeterminedvalue at which this jiggling can be suppressed, or in other words at asmaller current value than that of the map M3.

Hence, the command value calculating unit 3 calculates the current valueI serving as the control command value for the damper D on the basis ofthe vibration level r and the stroke speed Vd by referring to the mapsM1 to M4, and outputs the calculated current value I to the driving unit5. The driving unit 5 supplies a current to the damping force adjustmentunit 4 of the damper D in accordance with the current value I.

The damping force adjustment unit 4 adjusts the damping coefficient ofthe damper D upon reception of a current amount corresponding to thecurrent value I from the driving unit 5. As a result, a damping forcecan be generated by the damper D in accordance with the stroke speed Vd.

The damping force of the damper D is controlled by the damper controlapparatus E in the manner described above. Moreover, the vibration leveldetecting unit 1 of the damper control apparatus E can detect thevibration level r in a timely fashion and in real time. As a result, atime delay between the occurrence of vibration in the object anddetection of the vibration level r can be reduced, and therefore thedamper control apparatus E is sufficiently suitable for use insuppressing vehicle vibration.

As described above, the damper control apparatus E controls the dampingforce of the damper D by selecting the map M1, M2, M3, M4 in accordancewith the magnitude of the vibration level r of the unsprung member W,and determining the current value I to be applied to the damping forceadjustment unit 4 from the selected map and the stroke speed Vd. In sodoing, as shown in FIG. 7, for example, the damper control apparatus Ecan cause the damper D to generate a damping force having an optimumdamping characteristic in accordance with the vibration level r.

A characteristic indicated by a solid line in FIG. 7 is a dampingcharacteristic obtained when the map M1 is selected, and acharacteristic indicated by a dotted line in FIG. 7 is a dampingcharacteristic obtained when the map M2 is selected. Further, acharacteristic indicated by a dot-dash line in FIG. 7 is a dampingcharacteristic obtained when the map M3 is selected, and acharacteristic indicated by a dot-dot-dash line in FIG. 7 is a dampingcharacteristic obtained when the map M4 is selected.

When the vibration level r is low, medium, or high, the dampingcoefficient increases in accordance with the magnitude of the vibrationlevel r such that the damping characteristic of the damper D is optimumfor the vibration level r. Additionally, a damping force obtained whenan absolute value of the stroke speed Vd is in the vicinity of 0decreases as the vibration level r increases, and therefore thepassenger comfort of the vehicle can be improved while avoiding rapidvariation in the damping force during a switch in the damper D betweenexpansion and contraction.

Furthermore, in a condition where the vibration level r is small suchthat the damper D vibrates slightly, the map M3 is selected so that whenthe stroke speed Vd is in transition in the vicinity of 0, the dampingforce generated by the damper D is increased. In so doing, throbbingvibration in the unsprung member W can be suppressed sufficiently sothat throbbing vibration is not transmitted to the vehicle passengers.Moreover, when the vibration level r is 0, the map M4 is selected suchthat the current value I is suppressed, and therefore a jiggling in alower frequency band than the throbbing vibration is not transmitted tothe vehicle passengers. As a result, a reduction in passenger comfortdoes not occur.

As described above, the damper control apparatus E includes thevibration level detecting unit 1 configured to detect the vibrationlevel r, the vibration level r serving as the magnitude of the vibrationof the unsprung member W, the stroke speed detecting unit 2 configuredto detect the stroke speed Vd of the damper D, and the command valuecalculating unit 3 that determines the control command value I on thebasis of the vibration level r and the stroke speed Vd.

Accordingly, an optimum control command value can be determined inaccordance with the magnitude of the vibration, and damping forcecontrol corresponding to the magnitude of the vibration of the unsprungmember W can be performed. As a result, passenger comfort in the vehiclecan be improved.

Further, with the damper control apparatus E according to thisembodiment, when the vibration level r is high, the incline of thecharacteristic between the control command value and the stroke speed Vdincreases.

Accordingly, the control command value generated when the stroke speedVd is in the vicinity of 0 decreases, and therefore rapid variation inthe damping force during a switch in the damper D between expansion andcontraction can be alleviated. Hence, noise generated in a vehicle cabinwhen vibration is applied to a vehicle body, as well as shock exerted onthe vehicle body, can be avoided so that the vehicle passengers do notexperience discomfort. As a result, the passenger comfort of the vehiclecan be improved even further.

Furthermore, with the damper control apparatus E according to thisembodiment, as the vibration level r decreases, the incline of thecharacteristic between the control command value and the stroke speed Vddecreases, and therefore the vibration of the unsprung member W can bedamped reliably when the stroke speed Vd increases, leading to anincrease in the vibration level r. Conversely, in a case where thevibration level r is high, the damping force of the damper D does notbecome excessively large when the stroke speed Vd is in a low speedregion, and when the stroke speed Vd is in a high speed region,passenger comfort in the vehicle can be improved.

Moreover, the damper control apparatus E is configured to hold theplurality of maps each representing the relationship between the currentvalue I serving as the control command value and the stroke speed Vd inthis embodiment. The command value calculating unit 3 selects one or twomaps from the plurality of maps on the basis of the vibration level r,and determines the current value I on the basis of the selected map andthe stroke speed Vd. As a result, the current value I serving as thecontrol command value can be determined extremely easily.

Furthermore, to ensure, as a failsafe, that a certain degree of dampingforce is generated when the current value supplied to the damping forceadjustment unit 4 is 0, the damping force adjustment unit 4 may bedesigned so that a relationship between the value of the currentactually supplied to the damping force adjustment unit 4 and the dampingcoefficient of the damper D is as shown in FIG. 8, for example.

In FIG. 8, this relationship is set so that when the current value is 0,the damping coefficient takes a larger value than 0, when the currentvalue is i1, the damping coefficient takes a minimum value, and in arange where the current value exceeds i1, the damping coefficientincreases in proportion with the amount by which the current valueexceeds i1.

The current value I employed when the vibration level r is 0 may bedetermined at a value equal to or greater than the current value i1after checking a balance between the current value I and the comfort ofthe vehicle passengers, and a map having an intercept according to whichthe current value I increases as the vibration level r increases may beset from the determined current value. Further, in a case where thedamping coefficient of the damper D is reduced steadily as the currentamount supplied to the damping force adjustment unit 4 increases, a mapon which the current value I decreases as the vibration level rincreases may be set. In other words, the maps may be set as desired inaccordance with the design of the damping force adjustment unit 4.

Although not shown in the figures, it should be noted that the dampercontrol apparatus E according to this embodiment includes, as hardwareresources, an A/D converter for taking in the signals output by thesensor units, and a storage apparatus such as a ROM (Read Only Memory)storing a program used in the processing required to detect thevibration level r and calculate the current value I, for example. Thedamper control apparatus E may further include a calculation apparatussuch as a CPU (Central Processing Unit) that executes the processingbased on the program, and a storage apparatus such as a RAM (RandomAccess Memory) that provides the CPU with a storage area. Operations ofthe vibration level detecting unit 1 and the command value calculatingunit 3 may be realized by having the CPU of the damper control apparatusE execute the program.

In the above description, the current value I applied to the dampingforce adjustment unit 4 is used as the control command value, but adamping force target value to be generated by the damper D may be usedas the control command value instead. In this case, the damper D may becaused to generate a damping force corresponding to the damping forcetarget value by converting the damping force target value into a currentcommand and applying the current command to the damping force adjustmentunit 4. In this case, a relationship between the stroke speed and thedamping force target value may be plotted on a map and used in place ofthe map representing the relationship between the stroke speed and thecontrol command value.

Furthermore, in the above description, the control command value isdetermined using a map, but the control command value may be determinedusing a function having the vibration level r and the stroke speed Vd asparameters. In this case, the damper control apparatus E need notexecute a map calculation, and therefore the plurality of mapsrepresenting the relationship between the control command value and thestroke speed Vd need not be held in the damper control apparatus E.

Alternatively, the vibration level r of the unsprung member W may bedetected by providing the stroke sensor 26 in the damper D, as shown inFIG. 1, for example, and setting one parameter from the relativedisplacement between the cylinder 12 and the piston rod 14, detected bythe stroke sensor 26, a relative speed obtained by differentiating therelative displacement, and a relative acceleration obtained bydifferentiating the relative speed as the first reference value a. Then,by extracting a component that matches the resonance frequency of theunsprung member W from the first reference value a using the filter 23,one of the displacement, the speed, and the acceleration of the unsprungmember W in the up-down direction can be obtained. Furthermore, a sensormay be attached to the unsprung member W such that the up-down directionacceleration of the unsprung member W is detected directly, and thisacceleration may be used to determine the first reference value.

When detecting the vibration level r of the unsprung member W, the thirdreference value may be obtained on the basis of the first referencevalue in addition to the first reference value and the second referencevalue. The final vibration level r may then be determined by calculatingthe first vibration level on the basis of the first reference value andthe second reference value and calculating the second vibration level onthe basis of the first reference value and the third reference value.

An embodiment of the present invention was described above, but theabove embodiment is merely one example of an application of the presentinvention, and the technical scope of the present invention is notlimited to the specific configurations of the above embodiment.

This application claims priority based on Tokugan 2013-050130, filedwith the Japan Patent Office on Mar. 13, 2013, the entire contents ofwhich are incorporated into this specification by reference.

1. A damper control apparatus for damping vibration of an unsprungmember by controlling a damping force of a damper in a vehicle, thedamper being interposed between a sprung member and the unsprung member,the damper control apparatus comprising: a vibration level detectingunit configured to detect a vibration level, the vibration level servingas a magnitude of vibration of the unsprung member; a stroke speeddetecting unit configured to detect a stroke speed of the damper; and acommand value calculating unit configured to determine a control commandvalue on the basis of the vibration level of the unsprung member and thestroke speed of the damper, the control command value being a commandvalue for controlling the damping force of the damper.
 2. The dampercontrol apparatus as defined in claim 1, wherein the command valuecalculating unit determines the control command value so that an inclineof a characteristic line between the control command value and thestroke speed of the damper increases as the vibration level of theunsprung member increases.
 3. The damper control apparatus as defined inclaim 1, wherein the damper control apparatus is configured to hold aplurality of maps each representing a relationship between the controlcommand value and the stroke speed, and wherein the command valuecalculating unit selects a map from the plurality of maps on the basisof the vibration level of the unsprung member, and determines thecontrol command value on the basis of the selected map and the strokespeed detected by the stroke speed detecting unit.
 4. The damper controlapparatus as defined in claim 1, wherein the vibration level detectingunit includes: a first reference value acquiring unit configured toobtain a value of one parameter from at least a displacement, a speed,and an acceleration of the unsprung member as a first reference value; asecond reference value acquiring unit configured to obtain a secondreference value, the second reference value corresponding to adifferential value or an integral value of the first reference valueobtained by the first reference value acquiring unit; and a vibrationlevel calculating unit configured to determine the vibration level ofthe unsprung member on the basis of the first reference value and thesecond reference value.
 5. The damper control apparatus as defined inclaim 4, wherein the vibration level calculating unit determines thevibration level on the basis of a value from which a length of aresultant vector can be recognized, the resultant vector being obtainedon the basis of the first reference value and the second reference valuewhen the first reference value and the second reference value areplotted on orthogonal coordinates.